The military commander of the Abbott government’s border protection operation says the Australian authorities have bought no Indonesian fishing boats since the change of government because Jakarta has made it clear it does not support the policy.

The Coalition proposed at the federal election a scheme of buying up boats in Indonesia as a measure to disrupt people smugglers.

But Lieutenant General Angus Campbell told a Senate estimates hearing on Tuesday no Indonesian boats had been bought since the government launched Operation Sovereign Borders – a fact that the immigration minister, Scott Morrison, had so far declined to disclose.

Campbell said Indonesia had made it clear boat buying was not a measure it was interested in pursuing “at this point in time”.

“These measures, the one you’re referring to, isn’t one the Indonesian government wishes to see being applied right now as part of our co-operative activities, which we respect,” he said in response to a question from the Greens senator Sarah Hanson-Young.

Campbell said the policy remained on the table should Indonesia's attitude change.

The commander faced a combative hearing in the late afternoon once it became clear he intended to refuse to answer specific questions about recent operations involving asylum seekers.

Campbell told the Labor senator Kim Carr he did not intend to provide “incidental” reporting of specific border protection incidents because decisions had been taken about the best means of achieving the broader policy objectives.

He told the hearing he did not believe in “secrecy for secrecy’s sake” but it was justifiable, in his view, to protect Australian border protection personnel and regional relationships.

He said the current means of reporting the outcomes of border protection operations struck a balance between the public’s right to know and the operational requirement to keep details under wraps.

The current procedure is to hold a briefing once a week and provide specific comment if serious incidents warrant it.

Carr had been asking about a recent incident which has been the subject of media interest, when a Customs boat reportedly rescued a group of asylum seekers after first ripping away the bow of the boat.

Campbell declined to engage in specifics and emphatically rejected the idea that Operation Sovereign Borders had embroiled the military in politics.

“I am not involved in the political process. My job is to provide confidential advice to the government of the day and to implement those policies of the government.”

Immigration officials later dealt with questions about the number of pregnant women now detained offshore. There are eight pregnant women on Nauru.

Separate to the estimates process, the Coalition defied a Senate order to table material relating to its on-water operations.

Last week the Senate passed a motion requiring the immigration minister to produce documents he had wanted to keep secret outlining the border protection operations in Australia’s north.

Morrison made it clear he would not be complying with that order on national security grounds.